Frame repair / bonding

once glued you might try pinning it too (prepare holes before gluing) - this will hep it stay together when curing too - if you do it quickly enough after gluing.

• a bolt or 2 will work but drill and tap the lug (and the carbon) and put in grub screws and it'll be a flush job -you could even sink them in a little and cover them with something to hide them. (that depends on how long is the lug and how thick are the lug walls ?)
  
  

not as sightly but - alternatively - or as well as the above - fit some sort of cir clip around the tube (you may need to make tiny slits -like this http://www.sjscycles.co.uk/use-seat-post-shim-272-mm-id-prod22922/ - in the carbon end so it'll clamp onto the lug instead of just compressing and cracking the carbon )